Published April 2014
This Review presents a technoeconomic evaluation of ethylene production from the oxidative coupling of methane (OCM) based upon the technical information and data available in patents assigned to Siluria Technologies Inc. on the subject. It should be noted that this is a first-of-its-kind plant conceptualized by Siluria and it has not yet been commercialized.
In this review, one million metric t/yr of polymer grade ethylene is produced via OCM. The OCM reactor consists of a two-stage adiabatic, axial fixed bed reactor that utilizes Siluria’s proprietary nanowire catalyst to convert methane and oxygen to ethylene at around 1000°F and 130 psia. The methane feed to the OCM reactor is the recycle stream from a downstream demethanizer overhead supplemented by CO and CO2 conversion to methane in a two-stage methanation reactor. The hot OCM effluent from the second-stage effluent is mixed with heated, recycled ethane from a downstream C2 Splitter and cracked to convert ethane, primarily into ethylene. Hot reactor effluent is used to heat the OCM reactor feed, generate high-pressure steam and heat process condensate. Cold reactor effluent is compressed and mixed with sulfur-free pipeline natural gas and treated to remove CO2 and H2O prior to cryogenic separations. The treated process gas is fed to a demethanizer column to recover 99% of the ethylene. The demethanizer bottoms stream is separated in a deethanizer column to separate C2s from C3+ components. Deethanizer column overhead is first treated in a selective hydrogenation unit to convert acetylene into ethylene and ethane using H2 from a pressure swing adsorption (PSA) Unit. The resulting stream is separated in a C2 splitter unit to separate ethylene from ethane. The deethanizer bottoms stream is sent to a depropanizer to obtain refinery-grade propylene (RGP) and a mixed C4+ stream, both of which are sold for credit. The ethane product stream from the C2 splitter bottoms is recycled to the second stage of the OCM reactor to complete extinction. Polymer-grade ethylene product (99.96wt% ethylene) obtained from the C2 splitter overhead is compressed to 1,000 psig and exported as product.
Our cost analysis is based on a plant producing one million metric t/yr of ethylene at a 0.95 stream factor (equal to an installed capacity of 1.059 million metric t/yr). Cost estimates, details thereof and relevant assumptions are provided in this Review.